Exhaust systems for marine engines generally include an exhaust manifold connected to the engine at each row (or “bank”) of engine cylinders, and a corresponding exhaust conduit coupled to the exhaust manifold for directing exhaust gases from the manifold to an exhaust outlet. In conventional exhaust systems, the exhaust conduit includes a horizontally oriented catalytic converter assembly having a catalyst that removes harmful emissions from the exhaust gases before being expelled through the exhaust outlet.
Exhaust systems can experience extremely high temperatures during use. For example, the core temperature of a catalytic converter in a conventional exhaust system can reach upwards of 1,000 degrees Fahrenheit (° F.) or more. For safety purposes, the U.S. Coast Guard requires that exterior surface temperatures of marine engine exhaust systems be maintained below 200° F. Accordingly, components of conventional marine engine exhaust systems, including the catalytic converter assemblies, are often liquid-cooled to ensure safe and compliant operating temperatures.
Marine engines are susceptible to being damaged through the introduction of water through the exhaust system into the marine engine. One way through which water may enter a marine engine is through what is known in the industry as “reversion”. Reversion is the reverse flow of exhaust gases during the time period in which both intake and exhaust valves of the marine engine are simultaneously open. Pulses in the exhaust system cause water to move backwards into the exhaust manifold. Reversion primarily occurs when the marine engine runs at idle speed or slightly above idle speed.
Water injected into a marine engine typically damages an exhaust valve thus preventing the cylinder with the damaged exhaust valve from correctly sealing. This damaged cylinder then causes water to be pulled into the marine engine through the damaged exhaust valve. The introduced water is distributed within the marine engine causing the ultimate failure of the marine engine.
One known type of marine engine exhaust system design that seeks to minimize reversion uses connected conduits from a pair of exhaust manifolds, one exhaust manifold being located on each side of the marine engine. Gas pulses from each conduit are combined and the combination subsequently combined with cooling water. This type of marine engine exhaust system seeks to combine pulses from both sides of the engine so that double the number of pulses are present when the marine engine runs at idle speed or slightly above idle speed. Unfortunately, the exhaust gases in such a system are extremely hot because water is not added until after the gases combine which increases backpressure on the marine engine.
Accordingly, there is a need for improvements to known marine engine exhaust systems to reduce reversion.